1. Field of the Invention
This invention relates generally to printers that are adapted for use with handheld computers and, more particularly, to portable printers that are adapted to receive and carry portable, handheld teletransaction computers or data terminals.
2. Description of the Related Art
Portable printers adapted to receive and carry handheld computers or data terminals typically include a housing and associated carrying handle, a printer mechanism with a platen, a printing element and paper supply, a cradle and associated connector for receiving a handheld computer, and a power supply, an internal battery and a power cord for charging or ac operation. When the computer is received in the cradle, the printer connector automatically engages a connector of the computer. Data stored in the computer then can be printed in readable format onto the paper.
Portable printers of this kind sometimes are used to carry a handheld computer at a work site. While information is being entered into the computer, the printer is simultaneously providing a readable printout of the entered data. At other times, data is entered into the computer prior to its being received in the printer cradle, and a readable copy of the previously entered data is produced at a later time. For example, handheld computers and portable printers often are used by delivery personnel to record data relating to successive deliveries and pickups and to provide a printout or invoice for each delivery or pickup. The printer must be capable of being transported to work sites where it is needed and also capable of enduring harsh environmental conditions. Therefore, it is very important that the printer be small durable and lightweight. In addition, if the portable computer and printer ordinarily are to remain connected together, it is preferable that the printer provide some degree of external protection for the computer.
The mating engagement of the printer connector and the portable computer connector must be secure and positive, and must stand up to thousands of coupling cycles without deterioration. One of the two connectors typically includes many small, parallel metal connecting pins that are received by complementary conductive connecting bores in the other connector. Unfortunately, these connecting pins can be bent, or even broken, after many cycles of use. Efforts have been made in the past to reduce the possibility of so damaging the pins and thus reduce the frequency with which the printer must be serviced. Although such efforts have generally been considered successful, it is believed that a further reduction in the need for printer servicing is attainable.
Portable printers of this kind have been powered by multiple power sources, including an internal dc power supply receiving its power from an ac power cord, an external dc power source delivering power to the printer via a power connector, and an internal battery. Unfortunately, no convenient or automatic means for selecting from these various power sources is believed to have been available. This has led to time-consuming manual selections and to unnecessary drains on the internal battery.
It should therefore be appreciated that there is a need for an improved portable printer for use with a handheld computer or data terminal that has greater flexibility in its interfacing with the computer, while reducing the need for servicing its interface components, and it also should be appreciated that there is a need for an improved means for automatically selecting between the printer's various sources of power. The present invention satisfies these needs.